Washington head coach Chris Petersen had to explain what a fullback was to his defense as they prepped for next opponent

Washington and Stanford will meet on Friday in a critical Pac-12 matchup.

Stanford is one of the few teams in college football that still runs an offense that includes a fullback.

Ahead of the game, Washington head coach Chris Petersen told reporters he had to explain the concept of the position to his defense.

The Washington Huskies will take on the Stanford Cardinal on Friday night in a matchup of Pac-12 powerhouses that could very well determine whether or not the conference is represented in the College Football Playoff this year.

The Huskies are the Pac-12's best hope to make the playoff, with just one loss to their name and a fairly strong schedule remaining that includes Friday's game against Stanford, a matchup with Washington State during rivalry week, and if all goes according to plan, the Pac-12 title game. If Washington can win out, there's a chance they sneak back into the playoff with some help from around the college football world.

But before making any postseason plans, they'll have to get through a Stanford team that presents them with a challenge the likes of which they've never seen: fullbacks.

While taking questions from reporters, head coach Chris Petersen revealed that he had to explain the concept of a fullback to his defense earlier in the day.

"I would like to play (against) something we've seen a whole bunch of where you get those carry over reps," Petersen said. "There's a lot of stuff (Stanford does) we haven't seen anything like that, so we got to be able to get lined up correctly and play a fullback. We explained what a fullback is to our defense today. They were very intrigued."

You can watch Petersen's comments below.

As you can see, Petersen delivers the line in a half-joking tone, but it's likely not that far from the truth. Stanford runs a throwback smash-mouth offense that was once the norm across the college football landscape but has now been largely abandoned in favor of the spread and other systems more conducive to passing. But Stanford's system has been highly successful this year, with fullback Daniel Marx leading the way for running back Bryce Love to average an astonishing 9.6 yards per carry.

Washington and Stanford kicks off at 10:30 p.m. ET on Friday night. Hopefully the Huskies defense have fully grasped the new concept by then.